1. Field of the Invention
The present invention generally relates to identification systems and more particularly to wireless identification systems that utilize electronically sensitive tags to store and provide identification information.
2. Background Information
Radio Frequency Identification Systems (RFIDs) are used in a variety of industries to identify, track, and provide various other types of information related to the items upon which the tag is placed. A typical RFID system is usually made up of at least one transmitting and receiving device commonly called a reader and at least one passive or active target device, typically called a tag. The basic principal of this system involves the transmission of radio frequency energy from the reader to the tag. The tag receives the signal, modifies that energy and reflects this modified signal back to the reader, where the reflected and modified return signal is received, read and decoded. Some configurations also contain writers which enable various forms of information to be written back on to the tag.
RFID systems can be used in a variety of applications. Most typically these systems are utilized in a configuration where a tag is typically placed upon something that moves and a reader is placed in the hands of a person who seeks to determine information regarding the item upon which the tag has been placed. In some instances, the tags have their own internal power source while in other circumstances the power to power the tag and transmit the signal are derived from the reader itself.
Most tags contain a receiver and modulating device for transmitting a modulated signal back to the reader. The reader contains an antennae means for receiving information from the tag and reading this information. The transmission of information and power between the reader and the tag is typically accomplished by the modulation of the RF carrier. In many instances the tag is what is called a passive tag, which receives power to modulate the signal only through the receipt of transmission material from the reader. In these instances the reader is maintained in the ON state to provide power to the passive tags and is pulsed off and on for short intervals following the prescribed modulation timing and amplitude variations of the specific tag classification.
Some passive tags incorporate a capacitive storage mechanism to provide the required power for these pulse intervals. In the reverse direction, (the transmission from the tag back to the reader is also referred to as the reverse link) information is oftentimes transferred using a backscatter technique. In this backscatter technique, radio frequency (RF) energy incident on the tag antennae is modulated by changing the impedance of the antenna and effectively changing the radar cross section (RCS) of the tag and the amplitude of the energy reflected back to the reader.
In other instances, the tag impedance is such that the tag absorbs the RF energy, which is then used to power the tag. The tag changes the antenna impedance following the timing requirements of the specific tag classification effectively increasing the reflectivity of the tag and amplitude of the backscattered carrier received at the Reader. In these systems, the reader provides power to passive tags by maintaining a constant RF carrier throughout the entire transaction with the tag.
In some circumstances, this constant sending of a signal combined with the backscattered response signals can be problematic particularly in applications where the reader is in close association with a plurality of tags or when the reader and the tags are in close contact with one another. This close association of the tags can cause the compression of signals as well as the compression of the modulated signals emanating from these tags. This results in signals which are difficult to separate or individually ascertain. Various attempts to separate these signals and these tags have proved to be either too expensive or technically unsuitable for use in such a system.
These weaknesses in the present systems have made the programming of RFID labels from a single location or device very difficult. Where such systems have been implemented, the equipment utilized to achieve these results has been too expensive to allow for widespread use of this technology or the use of this technology in conjunction with the many items in common commerce.
Attempts at designing a system and device that can be utilized in close areas have included the use of separate antennas, to each transmit and receive signals from the device. However, this methodology typically requires a large area to implement and further requires site specific research to evaluate the amount of isolation that can be achieved in a specific production environment. Other attempts at providing a low cost RFID tag with the required specificity have included the use of a ferrite circulator or a three decibel coupler to provide increased isolation between well-terminated ports. However, the cost of these parts makes them so expensive so as to reduce their applicability and use in various aspects of industry or commerce.
Therefore what is needed, is a low cost RFID system which allows individual tags to be isolated, selected, programmed and verified. Preferably, this system should be made of inexpensive parts, which allows the device to be manufactured cheaply and thus used in a broad range of applications. This low cost RFID system should be able to function in close environments even in the presence of other tags. The present invention provides these advantages and does so in a way that is sufficiently reliable and cost effective so as to be accessible and useful in a variety of varying embodiments.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.